Separation of hydrocarbons from nonhydrocarbons by diffusion



3 Sheets-Sheet l Eoomlzmoomtz Q mnomooo J. P. JONES IN VEN TOR. JEAN P. JONES BY M1 y? Ay'ToRNEYs SEPARATION OF HYDROCRBONS FROM NONHYDROCARBONS BY DIFFUSION Nov. 1l, 1952 Filed April 15, 194e mzmm mm,

wDOmOn. IZOZ IUEIZMOIZ III! J P JONES SEPARATION OF HYDROCARBONS FROM NONHYDROCARBONS BY DIFFUSION 6 A. 9 l 9 w 1 1 ,l i m5 n w A omo. v. .w ul Q No u. @WQ QB. om zwoomtz F Nov. 11, 1952 J. P. JONES 2,617,493

SEPARATION oF HYnR'ocARBoNs FROM NoNHYDRoCARBoNs BY DIFFUSION Filed April 15,'1946 z` sheets-sheet s CONCENTRATED ODOROUS COMPOUND IN V EN TOR. 4 JEAN FY JONES ATTORNEYS Patented Nov. 11, 1952 SEPARATION OF HYDROCARBONS FROM NONHYDROCARBONS BY DIFFUSION Jean P. Jones, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application April 15, 1946, Serial No. 662,151 12 claims.' (o1. 18s- 115) This invention relates to the removal of nonhydrocarbon constituents from hydrocarbon materials. In one embodiment of this invention it relates to the removal of inert materials such as nitrogen, oxygen and/or water from hydrocarbon materials. In another embodiment of the invention it relates to the removal of odorous compounds Vsuch as volatile mercaptans, volatile oxygen-containing compounds, such as aldehydes of low molecular weight, hydrogen sulfide, and the like, Afrom hydrocarbon materials. Still another embodiment of this invention relates to the removal of both of said undesired types of said materials from hydrocarbons. In speciic applications of each of the foregoing embodiments of the invention, preferred embodiments relate to the treatment of normally gaseous mixtures in which the hydrocarbons are paralin hydrocarbons and which are essentially free from unsaturated hydrocarbons, such asY olens, diolens, acetylenes, aromatic hydrocarbons, and the like.

I have found that non-porous membranes can be used to eiiect separations such as just discussed. I have also found that undesired compounds oi the class consisting of nitrogen, oxygen and water are less soluble in certain types of nonporousmembranes than are hydrocarbon materials and that certain hydrocarbon materials, especially the normally gaseous paraiiin hydrocarbons, are less soluble in similar membranes than are odorous compounds such as formaldehyde, low-boiling mercaptans, hydrogen sulde, and the like.v The membranes which can be used in the practice of my invention have rubber as a base, although they generally are not pure rubber since it is preferred that the rubber be compounded with other materials, such as carbon black, sulfur, and sulfur compounds. By rubber I intend to include natural rubber and various typ-es of synthetic materials now well-known to the art as synthetic rubber, such as polymers of butadiene and its homologues and derivatives, rubber-like olefin polymers such as those formed from isobutylene at low temperatures in the presence of a Friedel-Crafts type catalyst, polymers between these hydrocarbons just mentioned and other-.unsaturated organic compounds, such as acrylic acid and its homologues, derivatives and esters, acrylonitrile, and the like. Many of such synthetic rubbers are not highly suited for use in my invention since the hydrocarbon materials discussed herein are not as soluble in such rubbers as they are in other rubbers. On the other hand, where the solubility and chemical characteristics of the materials undergoing treatment 2 are such that the rubber is unduly swelled and structurally weakened by having the hydrocarbons and/or odorous compounds dissolved therein, such rubbers, or compounded materials, will not be well suited to use in the invention. The most favorable material for use in the treatment of any particular mixture can be readily selected from the results of sample tests made in the light of the present disclosure.

It is an object of my invention to remove nonhydrocarbon impurities from hydrocarbon-containing mixtures. y Y

Another object of my invention is to reduce the odor in hydrocarbon-containing materials.

Still another object of my invention is to reduce the nitrogen content of normally gaseous mixtures containing nitrogen and normally gasef ous parain hydrocarbons.

Further objects and advantages of my inven-l tion will become apparent to one skilled in the art from the accompanying disclosure and discussion.

The objects of my invention are attained by contacting a hydrocarbon-containing mixture,

such as is discussed herein, with a, relatively non-.-

porous membrane under conditions such that the components of the mixture which are the more soluble in the material of which the membrane is constructed dissolve in the membrane, and are removed from the opposite side of the membrane in a higher state of relative concentration than they are present in the mixture initially contacted with the membrane. The process of each of the various modications of the invention is ponent of the charged mixture which is the more soluble in the material from which the membrane is made. The other zone of each of said stages is referred to herein and in the claims as a diffusate zone. This diiusate zone receives the components of the mixture introduced into the dilusion zone solely by passage of said materials through the membrane, and primarily by evaporation from the surface of the membrane, and

there is discharged from this `diiiusate zone a material which is relatively richer in the compo-v nent of the said mixture which is the more solu-v Each of these stages comprises two ble than the substance from which the membrane was made. Although the terms diffusion and diffusate are used herein, it is to be clearly understood that such terms are based upon diffusion of solute molecules in solution in the membrane material, which is the solvent.

The mixture' charged to each stage may be charged thereto either in the liquid state, or in the gaseous state, or as a physical mixture of liquid and gas. However, preferred operation is carried out with the introduction of such a mixature in the gaseous state. In thevmost preferred operation the material present in the difusate zone is present therein and removed Vtherefrom in the gaseous state. This removal may be effected by continuously maintaining an appreciably lower total pressure in the diifusate zone `than that maintained in the diifusion zone. n sired, however, substantially the same total pressure may be maintained in both zones by introducinginto the diiusate zone a substance which is substantially insoluble in the material from which the membrane is made and which is more readilyseparated from the component being concentrated in the diffusate zone than are the components of the mixture charged to the diffusion zone. In' such a case the partial pressure of the material being concentrated in the diffusate zone will be appreciably lower than is its'partial pressure in the diffusion zone.

The membrane whichv separates the two zones in each stage should be substantially non-porous, that is, the process of the invention is carried out so that the material whichV passes through the membrane does so by virtue of being dissolved in the membrane and being removed from the resulting solution from the opposite side of the membrane. Passage of materials through. the membrane by virtue of diiferences in average molecular speeds of gaseous molecules, due to differences n molecular weights, should play no more than a negligible role, if any, in the process of the invention as practiced. For this reason mixtures which contain appreciable proportions of hydrogen and/or helium are not suitable for separation in accordance with my invention since the average ymolecular speeds ofthe molecules of these elements are so much higher than those of other compounds that they tend to offset the operation of the process even when non-porous membranes are used.

The membranes used in the practice of this invention should be as thin as is practicable while at the same time maintaining an essentially nonporous character. Membranes thinner than about 0,0001 inch are generally not practicable while membranes thicker than about 0.1 inch are generally so thick that the materials which dissolve in them take too long to pass through them and be removed from the opposite side by Vaporization. rIhis slows up the process and makes an extremely high gradient in the concentration of the dissolved material between the surface of the membrane on the diffusion-zone side and the surface of the membrane on the diffusate-zone side. Preferably the membrane will be between about 0.0005 and about 0.005 to 0.01 inch. When there is a high pressure differential between the two sides of the membrane it is necessary to support the membrane by some relatively strong mechanical support, such as a wire screen, or a grid, or a porous wall of ceramic material. The latter is the less desirable since the material vaporizing from the lowpressure sideof the membrane does not' have ready access to the space inthe diiTusateV If de 4 zone. If desired the supporting grid and the membrane may be manufactured together as an integral structure or the membrane may be laid against a separate support. It is preferred that the membrane, if it is made of an elastic material, be not greatly stretched since its use in the process of my invention tends somewhat to weaken it structurally. The pressure in the diifusate zone may be any desired pressure which is such that the partial pressure of the material which is more soluble in the membrane is lower in the diusatezone than it is in the diifusion zone. A high pressure or partial pressure) in the diffusion zone promotes solution of the more soluble component in the membrane, while a low pressure (or partial pressure) in the diifusate zone promotesremoval of dissolved material from the membrane. Preferred operation is obtained when no extraneous material is introduced into the diffusate zone and when the partial pressure of the material being enriched in the diiusate zone is equivalent to between about 0.01 and about 0.5 times its pressure in the diffusion zone, preferably 0.05 to 0.2 times such partial pressure. Pressures in the diifusion zone may be between about 5 and about 500 pounds per square inch absolute.

The thickness of the diiusate zone is preferably such that there is not too great a pressure' differential between a point of discharge of material from the Zone and a point in the zone far thest removed from any such discharge point. It is preferred that such a pressure drop be as low as is practical and not greater than 10 per cent of the total pressure. The thickness of the diffusion zone should be such that there is not a large pressure drop between the inlet and discharge points of said zone and should be correlated with the width and length of the diffusion zonevso that there will be relatively uniform flow of the mixture passing through the zone. There should be a minimum of opportunity for recirculating currents within the diiusion zone. The mixture passing through the zone, either liquid or vapor, is preferably passed through under conditions of turbulent ow so thatas the concentration of the material more soluble in the membrane decreases, there will be adequate contact between the owing mixture and the membrane. One, or more than one, inlet and one, or more than one, outlet may be employed for the diiusion zone and likewise one, or more than one, outlet may be employed for the diffusate Zone. The temperature of the operation should be as high as is permissible, depending primarily upon the physical characteristics of the material which forms the membrane and upon the adverse effects of temperature, and of the material dissolved in the membrane, upon the physical strength of the membrane. A preferred temperature of operation will generally be found between about 50 and about 300 F.

Various modifications of my invention will now be described in connection with the accompanying drawings, which show diagrammatically various arrangements of the stages which can be used to advantage in the practice of various modications of the invention. Figure l illustrates the most simple arrangement of stages for separating a two-component mixture. Figures 2 and 3 represent somewhat more complicated arrangements which, however, can very often be used more satisfactorily than the arrangements shown in Figure 1. Figures 4A and'LiB illustrate an arrangement of stages for separating into their products the materials present in a three-component mixture.l In each of these drawings are shown a plurality of separation stages, each stage being `individually identified by a reference numeral. Each stage is composed of a diffusion zone A and a diiusate zone B, separated by a membrane C. Since it is desired to make the drawings as simple as possible, not all of the various lines or conduits through which materials pass have been individually identified with distinguishing characters, but in each instance wherea line has been individually identified a line carrying a discharged diiusate bears an identiiication character consisting of the numeral identifying the stage from which it comes plus the letter D, and a line carrying an eiiiuent discharged from a diffusion zone bears an identification character consisting of the numeral identifying the stage from which it comes plus the letter E. If necessary, 'any individual diffusion zone, diffusate zone or membrane can be identified by adding' the numeral identifying the individual stage before the letter A, B, or C, as the case might be.

Referring now to Figure l, the simplest modiiication of my invention is illustrated for separating a substantially two-component mixture into each of its desired components. While it is realized that the various hydrocarbons will have diierent solubilities in the membrane used in each separation stage, the hydrocarbons in the charge stock are considered collectively as one component and the non-hydrocarbon materials, such as nitrogen, oxygen or water on the one hand, or odor-ous materials on the other hand,

are in each case likewise considered as one component. A charge stock con-taining desired hydrocarbon and undesired less-soluble material, such as nitrogen, is introduced into the separation system through line I0 leading to the diffusion zone of stage I3. In this embodiment the separation is illustrated by means of 5 stages numbered from II to I5, inclusive. The stage from which a product of the process is discharged from the diffusion zone is indicated as being the lowest stage of the series and the stage from v which la product of the process is discharged from the diffusate zone is designated as being the highest stage o-f the series. In the process of Figure 1 the eiiiuent discharged from the diffusion zone of each stage except the lowest is passed to the diffusion zone of the next lowest stage and the diiusate from the diiusate zone of each stage except the highest is Ipassed to the charge of the diffusion zone of the next higher stage. It will be readily appreciated that any number of stages may be used, bo-th below and above the main-inlet stage, depending upon the characteristics of the membrane used with respect to the constituents to be separated, upon the temperature used in each stage, lthe pressure differential between the two zones of each stage, and upon the length of the path of the material flowing through each diffusion zone. In Figure 1 breaks have been shown in the lines joining adjacent stages to indicated that the numbell of stages may be increased or decreased at the points where breaks are shown. In the case under discussion a hydrocarbon material relatively po-or in nitrogen, or in many instances essentially free from nitrogen, is removed as a product of the process through line I5D and a nitrogen-concentrate poor in its hydrocarbon content is remo-ved as a produ-ct of the .process through line IIE. This material will contain a higher proportion of hydrocarbons, in most instances, than the .proportion of nitrogen conthis instance the desired hydrocarbon product is recovered through line I IE and the stream which contains a substantially higher proportion oi the odorous compound is discharged from the system through line I5D. The arrangement shown in Figure 1 is more suited to this latter type of operation th-an it is to the selective elimination of nitrogen.

The Iarrangement of separation stages shown in Figure 2 is one modification which is better for the elimination of nitrogen from a hydrocarbon-nitrogen mixture. A mixture comprising between about 70 or 80 lper cent gaseous parain hydrocarbons, primarily methane, with the remainder of the mixture being primarily nitrogen, is frequently found as a product of gas wells in certain area-s of the United States, notably the Texas Panhan-dle. Such a material can be successfully treated in the modification oi my invention illustrated by Figure 2, which compri-ses nine stages numbered 2I to 29. In this modication the charge is introduced through line 20, and the eiiluent discharged from the diffusion zone of the main-inlet stage 25 and from the diffusion zones of each of the lower stages is passedto the charge of the diffusion zone of the next lower stage.

with a nitrogen-rich efliuent being removed from the diffusion zone of the lowes-t stage, a-s through line 2 IE. The discharged difusate from each of these lower stages is passed to the charge of the diusion zone of the second higher stage. The diffusate discharged from the diffusate zone of the main-inlet stage and from the diffusate zone of each of the stages higher in the series is passed to the charge of the diffusion zone of the next higher stage in the series, with a nitrogenpoor hydrocarbon gas being removed from the diffusate zone of the highest stage as through line 29D. The effluent discharged from the diffusion zone of each of these higher stages is passed to the charge of the diifusion zone of the second lower stage. The process of Figure 2 has been illustrated by the use of nine separation stages but, as will be readily appreciated by one skilled in the art, any desired number of stages may be used, both above and below the maininlet stage. Below the main-inlet stage breaks have been shown in the lines which serve to connect stages 23 and 24 with the rest ofthe series. This illustrates that these two stages may be eliminated from the system with suitable joinder of corresponding lines, as by joining line 25E with line 23E, or additional stages may be inserted as may be desired in any particular instance. The removal or insertion of a group of two stages has been illustrated for reasons of simplicity, but it will be readily appreciated that the number of stages inserted or removed may be odd as well as even. A similar showing has been made in the series above the main-inlet stage, involving stages 26 and 27, and similar comments apply as have been discussed in conand 24.

.Another modification which is particularly suitablefor treating a normally .gaseous mixture such as discussed in connection Awith Figure 2., `s shown. :in Figure V3. Here again a series of nine stages, numbered 3| to 39, is illustrated with chargebeing introduced to the diffusion zone of intermediate stage 35 throughline 30. In this modification the eiiluent discharged from each of the .difiusion zones of yea-ch of the lentire series of stagesis passed'to the charge of the/diffusion zone of `the neXt lower stage, with la nitrogen concentrate being removed as a vproduct Iof the process through line 3|E. As in the modification shown in .the lower stages of Figure 2, the diiusate discharged from each diffusate Zone is Dassedto the charge of Vthe diffusion zone of the 'second higher separation stage, except that the diffuslate from the penultimate stage is passed to the highest stage, with `a nitrogen-poor hydrocarbon gas being removed as a product of the process through lineiSD. As with the other modification-s of my invention, a-ny desirable number of stages, either odd or even, may be used both --above and 4below the main-inlet stage.

In many instances it will be desired not only to remove nitrogen from a charge gas, such as is treated inthe modifications shown in Figures 2 and .3, but also Ato remove an odorous material, such as hydrogensulde and/or methyl mercaptan, or an aldehyde, from such a mixture. An arrangement-fof diffusionstages by which this can be accomplished shown in Figures 4A and 4B which, together, make one complete unit. In this modification rtwenty separation stages are usednumbered IUI to |20, In reality 'this series ofstages -is dividedinto three sections. One ysection for removing nitrogen is made up primarily of lstages ||l;| to |09, together with a portion of the stages in vother sections of the entire series. Anodor-removal section is made up primarily of stages H6 -to |20, although some stages of the other two sections contribute materially to the operation of this particular section. A hydrocarbon-concentration section is made up 'primarilyof stages to I5, but here again, stages in other sections also contribute materially to theoperaton Yof this Aspecific section. A mixture such as one containing about 14 per cent nitrogen, 85 per Vcent methane and ethane, of which at least 80 per vcent is methane, and containing about l per cent hydrogen sulde is charged to the process illustrated in Figure .4 through line |09 to the dilusion zone `of the main-inlet stage |09. The effluent discharged from this diffusion zone and from the diffusion lzone of each stage lowerin this series is passed tothe charge of the diffusion vzone of the next lowest stage, with an odorless nitrogen concentrate being removed as a product of .the process from the diffusion zone of the lowest stage through line IME. In this specic modification the difusate `discharged from the diffusate Zone of each of the stages below the main-inlet stage, except the two immediately below the inletstage, is passed to the charge of the diiusion zone of the third higher stage. The difusate discharged from the diiusate zone ofthe main-inlet stage |09 is passed'as theprincipal charge to an intermediate inlet stage ||3 of the odor-concentration section. This section operates substantially as does the apparatus illustrated inFigure 1 when this apparatus is used to. remove -an odorous material from a substantially .nitrogen-free ,hydrocarbon material. `'Ihe difiusatepassed from the dirfusate zone of stage.

|08 is passed through line |08D to the charge of a diffusion zone in a stage in this O dorfeoncentration lSection lower than .Stage l 8, such as to the charge of -stage through line; |0813 or,

if ,stage H1 is omitted or suppieinentarto the.

of the highest stage of the odor-concentrationsection, as through` line |'-20D.

LThe effluent discharged from the -dilusion .zone of the lowest stagein theodor-concentration section is passed las Ythe main charge vto the diffusion zone of an intermediate .Stage of thevhydrocar.- bon-concentration section, such. as y,stage The higher stages inV this section operate in the manner illustrated for the higher stages of "the process illustrated in Figure Y2, with a substantially odorless nitrogen-poor hydrocarbon gas being recovered as a product of the process from the diiusate Zone of the highest stage of this section, Yas through line ||5D. The eluen-t from the diffusion zone of the lowest stage of this hydrocarbon-concentration section is passed to the charge of .thedifusion zone of a stage which is lower inthe series than any stage from which a difusate is passed to the odor-concentration section of the entire series, such as by being passed through linesy HIE and HUE' to line IU'IE which enters dilusion zone Hlth.v

As has been donevin connection with Figures l, 2 and 3, breaks have been indicated in the lines joining .various Astages to indicate that the num-.- ber of stages may be increased or decreased at this point. Such an Aalteration in the number of.

stages maybe readily made by one skilled -in the art, in the light of the present disclosure. In view of the somewhat more complicated arrangement of stages below the main-inlet stage a change in operations by eliminating a group .of stages, such as stages |05, |01 .and |08, issome- `what more complicated. If .these three stages were to .be eliminated .the principles of the operation would not be changed in the least. The material flowing through the first .part of line ||l3D would continue .flowing through the last part of line HJSD; the material flowing .through the irst part of IMD would continue owing through `the last part of line |0'|D; the material flowing through the rst partof line |05D would continue to flow through line |081); and the ma.- terial flowing through the first part of LOSE would continue flowing through the last part of IGGE. Likewise, the material owing through line v|.||llil would continue owing through Vline IUE" instead of through line IDE as previously discussed.

Although it lis believed that more eicientoperation ,results from the arrangements of stages which jhave been discussed herein, itis to be `appreciated that various other modifications .and arrangements may be employed in the.;light of the present disclosure and discussion Without departing from the spirit of the invention. When attempting to separate nitrogen from hydrocarbons by employing the principles of the invention, it is preferred to pass the diffusate fromany one stage tothe diffusion zone of the stage which is a plurality of steps higher in vthe series, but Whether this be to the second higher stage as .illustratedin Figures 2 vand 3orto .the third higher 9 stages as illustrated in the left-hand portion of Figure 4, or to an even higher stage, will depend upon various factors discussed hereinbefore. The primary factor to be considered is, of course, the similarity of the composition of the diffusate to 5 the composition of the stream to which the diffusate is added. The diffusate should be added to that stream entering a diffusion zone which has a composition most nearly similar to said dilusate. The greater the difference in solubilil ties, between the hydrocarbons on one hand and the impurities on the other in the material used for membranes, the fewer the total' number of stages which will be necessary to effect a given extent of separation, the greater the differences l in compositions of diffusate and difusion-eluent streams from any one stage, and the greater the number of stages to be skipped in passing a diffusate back for admixture with a stream entering a diffusion zone. Likewise, whether or not the eiiluent from each of the diffusion zones passes to the next lower stage, as illustrated in Figures 1 and 3 and in parts of Figure 4, or whether the eluent from each diiiuson zone is passed to the second lower stage, or to an even still lower stage, as illustrated in the right-hand part of Figure 2 and in the hydrocarbon concentration section of Figure 4, will depend upon the same factors discussed hereinbefore. The process can be particularly applied to a normally gaseous mixture comprising 10 to 50 per cent nitrogen (by volume) with the remainder being parain hydrocarbons of which at least 80 per cent is methane. The product (hydrocarbon) resulting from treating such a mixture should con-f tain no more than about 5 per cent nitrogen. When the process is used to remove an odorous compound, this will generally not be more than about 5 per cent (by volume) of the charge stock, often not more than about 1 per cent. The hy-140 drocarbon product should be essentially free from the odorous material.

As will be readily appreciated by anyone skilled in the art, a number of compressors and/or pumps will be necessary for the successful opera- 745 tion of any modification of mv invention. In some instances itvmay be possible to operate with no compressor or pump on the effluent discharged from the diffusion zone of the maininlet stage or from Vthe diffusion zone of any ('50 lower stage, but a compressor or pump willbe necessary for substantially every other discharged product being passed from any Zone of any stage. If it is desired to operate any stage labove atmospheric temperature it will, of course, be necessary to supply suitable means for attaining and maintaining such a temperature. Since in many instances a diifusate may need to be increased in pressure by a substantial amount the temperature resulting from heat developed by such a compression may be higher than is suitable for the operation of the stage to which such a compressed diffusate is passed and means will need to be supplied for removing at least a part of heat developed by such a compression. Although vaporization is occurring from the surface of the membrane which bounds each diffusate zone, a process which requires a supply of latent heatgsolution is likewise taking place at the surface' of `,the same membrane which bounds the diffusion zone and such solution will generally provide all of the necessary latent heat when the mixtures 'oneach side ofthe membrane are both in the same physical state.V If the material on the diffusion side is liquid itis generally necessary to supply additional heat to maintain a satisfactory temperature of operation. Suitable compressors, pumps, control valves, temperature indicating and/ or control devices, heaters, coolers, flow-indicating and control devices, and the like, can be readily supplied by one skilled in the art, in the light ofthe present disclosure and discussion. Each stage may be composed of two simple chambers divided by a membrane, may be built up in sandwich form composed of three chambers, with the middle chamber being separated from each of the two outer chambers by a membrane, and with the middle chamber being either a diffusion zone or a diifu'sate'zone and the two outer chambers being either 'diifusate zones or diffusion zones, as the case may be, or the stage may be so constructed that the membrane is cylindrical in shape with either the diffusate Zone or the diffusion zone lying within the cylindrical space enclosed by the membrane and the other zone of the stage lying in the space outside of the cylindrical membrane. Various other modifications can be readily adapted by'one skilled in the art. Y

I claim:

1. A process for separating a mixture comprising primarily nitrogen and at least oneV normally gaseous parafn hydrocarbon into a nitrogenpoor hydrocarbon-rich fractionv and a hydrocarbon-poor nitrogen-rich fraction, which comprises introducing all of said mixture initially into an intermediate stage of a series of atleast five diffusion stages, each said stage comprising two zones separated by a non-porous membrane in which parainhydrocarbons are morev soluble than nitrogen with one of said zones being a diffusion zone receiving a nitrogen-hydrocarbon mixture as a direct charge and discharging a nitrogen-hydrocarbon mixture poorer lin hydrocarbons and with the other of said zones being a diifusate zone receiving hydrocarbons" only by diffusion through said membrane and discharging a gas having a hydrocarbon to Vnitrogen-'ratio higher than that in the charge to said diffusion zone, in the stages below the inlet ,stage passing a discharge from each of said diffusionzones except that of the lowest stage tothe charge of the diffusion zone in the next lower stage of said series and passing adischarged di'ffusate Afrom each of said diffusatelzones to the charge of. the diffusion zone of the second higher stage of said series, in the stages above .the inlet stage passing a discharge fromjeach of. said diifusion zones to the charge of theudiffusion zone in the second lower stage of vsaid series and passing a discharged diffusatefromv each of said diiusate zones except the highest tothe charge of the diffusion zone of the next higher stage of said series, removing from said highest stage a hydrocarbonrich diffusate fractionas a product of the process, and removing from the diffusionzone of the lowest stage of said series anitrogen-richfrac tion as a product of the process. 1 A y 2. A processfor separating almixture `comprising primarily nitrogen and at least one normally gaseous paraflin hydrocarbon into a nitrogen-poor hydrocarbon-rich,fraction and a hydrocarbon-poor nitrogen-rich fraction, which comprises introducing all of Y said mixture initially into an intermediate stage of a series of atleast five diffusion stages, each said stage comprising two zones separated by 'anon-porous.membrane in which parafnfhydrocarbons are moresoluble than nitrogen with` one of said`zones being`v a diffusion 'zone receiving a nitrogen-hydrocarbon f' garages :mixture .asa direct'charge'and discharging a n'ilnogen-hydrocarbon' mixture :poorer in hydrocarbons.' and with the other of said zones being a diffusate zoney receiving hydrocarbons only by diffusion through said membrane anddischarging Y a'gas having a hydrocarbon to nitrogen ratio higher than that in the charge to said diffusion zone, in the stages below the inlet stage passing a discharge from each of said diffusion zones .except that vof the lowest stage to the charge o the diffusion zone in the next lower stage of said series and .passing a discharged diffusate fromxeach :of said diffusate zones to the charge of the diffusionzoneaof a, higher stage which is atleast the second higher stage of said series, in

'the stages :above the inletstage passing a discharge' from each of said diifusion zones to the charge of .the diffusion zone in a lower stage which is' at least the second lower stage of saidseries and passing a discharged diusate from each of said diiusate zones except the highest to the charge ofthe diiusion VZone of the next higher stage of saidiseriesremoving from said highest stage a hydrocarbon-rich diffusate fraction as a. product of the process, and removing from the diffusion zoner of the lowest stage of said `series a nitrogen- ;r'ich fraction as a product of the process.

3. The process of claim 2 in which at least 80 per-'cent ofsaid parafn hydrocarbons comprise methane, the volume per cent of nitrogen in the charge is between about v50 and about 10 per centand in the hydrocarbon-rich product is not :greater than v5-per cent, Athe membrane is a substantially unstretched rubber having a thickness stages, each said stage comprising two zones separated by a non-porous .membrane in which parain `hydrocarbons are more soluble than nitrogenwith .one of said zones being a diffusion Vzone receiving -a nitrogen-hydrocarbon mixture as. a direct charge and discharging a nitrogenvhydrocarbon.mixture yrelatively poorer in hydrocarbons and withI the other of said Zones-being a 'higher than that iin 'the charge to said diffusion Yzone.passingfa discharge from each of said diffusion zones except that of lthe lowest stage to the charge of the diffusion zone in the next lower stage of said series, passing a discharged diiusateirom each of said diffusatezon'es except the `ilrsttwo to the charge of the diffusion zone o the second higher stage of said series, passing a discharged diiusatefromthe second from the top of `said stages to the charge of the diffusion zone ofthe highest stage, removing from said highest stage a hydrocarbon-rich diffusate .fraction as a product of the process, and removing from the diffusion zone of the lowest stage 'of said ser-ies a nitrogen-rich fraction as a product of the process.

VV5. A process for separating a mixture comprising primarily an undesired compound of the class consistingof nitrogen, oxygen and water and as desiredcompounds normallygaseousparan hy- `drocarbon's into a hydrocarbon-rich fraction and a hydrocarbon-poor fraction, which comprises introducing all of said mixture initially into an intermediate stage o'f'a series of at least five diffusion stages,r 'each said stage comprising two zones separated by a non-porous 'membrane in which parain hydrocarbons are more soluble than said undesired compounds with one of. said zones being a diffusion zone receiving such a mixture as a direct charge and discharging a mixture relatively poorer in 'hydrocarbons and with the other of said zones being a diffusate zone receiving hydrocarbons onlyy by diffusion through said membrane `andl discharging av gas relatively richer in paraiin hydrocarbons than that in the charge lto said diffusion zone, passing-.a dischargefrom eachof Asaid'diffusion zones except that of the l'oweststage to the charge of the diffusion lacne in the next lowerstage of said series,v passing a discharged diiusate-from each of said vdiiusate zones except the first two to the charge -of the -dif-usien zone of the second higher stage of said series, passing a discharged diifusate from the second from the top of said stages to `the charge of the diiusion zone of the highest stage, removing from said highest stage a hydrocarbonrich diffusate fraction as aproduct of the process, and removingl from the diffusion zone ofthe vlowest-stage of said series a hydrocarbon-poor frac- 0.01 and 0.5 times its partial-pressure in theocrresponding. diffusion :zone,iand in whichrthe temperatures of each said Istage is between-'about k50 `and about 200 F,

'7. The process of claim 4in which at least 80 per cent of the Aparaiiin hydrocarbons comprise methane, the volume per centofnitrogen-i-n the charge is between about 50 and about -l0 andthe volume per cent of nitrogen in the hydrocarbon product is not-greater than 5.

- 8. A process for separating amixture comprisingV primarily nitrogen and normally gaseous paraflin hydrocarbons into `a `nitrogen-poor hydrocarbon-rich fraction vand a hydrocarbon-poor nitrogen-rich fraction, which comprises introducing all Yof saidmixture initially into an intermediatev stage'of a series of at least three diiTusion stages, each said stage comprising two zones separated by a non-porous membrane in which parafn'hydrocarbons are more soluble than nitrogen with one of saidzones being a diffusion zone .receiving a nitrogen-hydrocarbonA mixture as a direct charge and discharging a nitrogenhydrocarbon mixture relatively poorer in hydrocarbons and with Ythe other -of said zones being a Vdiiusate zone receiving hydrocarbons only by diffusion through-saidmembrane and discharging a Agas having a hydrocarbon to nitrogen ratio higher than Athat in the charge to said ldiifusion zone, passing a discharge fromeach of said dii-usion zones except the lowest to the charge of a diffusion zone of a lower stage of said series, passing a discharged diffusate from each of said diffusate zones except the highest to the charge of a. diiusion zone of a higher stage of said series, removing from the Ydiffusion zone of said lowest stagea nitrogen-rich fraction as aproduct of the process, and removing from said highest stage a hydrocarbon-rich diiusate fraction as a product ofthe process. Y Y

1 brane in which paraffin hydrocarbons are more soluble than said undesired compounds with one of said zones being a diffusion Zone receiving such a mixture as a direct charge and discharging a mixture relatively poorer in hydrocarbons and with the other of said Zones being a diiTusa-te zone receiving hydrocarbons only by diiusion through said membrane and discharging a gas relatively richer in parain hydrocarbons than that in the charge to said diffusion zone, passing a discharge from each of said diffusion zones except the lowest to theV charge of a diiusion zone of a lower stage of said series, passing a discharged diusate from each of said diffusate Zones except at least the two highest to the charge of a diffusion zone of a higher stage which is at least the second higher stage of said series, passing a discharged diffusate from each of said excepted higher stages except the highest to the charge of a higher stage of said series, removing from the diffusion zone of said lowest stage a hydrocarbon-poor fraction as a product of the process, and removing from said highest stage a hydrocarbonrich diiusate fraction as a product of the process.

l0. The process of claim 8 in which at least 80 per cent of said parain hydrocarbons comprise methane, the volume per cent of nitrogen in the charge is between about 50 and about 10 per cent and in the hydrocarbon-rich product is not greater than per cent, the membrane is a substantially unstretched rubber having a thickness between 0.0001 and 0.01 inch, and the temperature of each stage is between about 50 and about 200 F.

11. A process for separating a relatively odorless hydrocarbon-rich gas from a normally gaseous mixture containing about 10 to about 50 per cent by volume of nitrogen, not more than about 5 per cent by volume of a volatile nonhydrocarbon odorous compound and the remainder normally gaseous parain hydrocarbons, which comprises introducing all of such a mixture into `an intermediate main-inlet stage of a series of at least thirteen diffusion stages, each said stage comprising two zones separated by a non-porous membrane in which said nitrogen, parai`n`n hydrocarbons and odorousompound are soluble with increasing solubility in the order named with one of'said zones being a diffusion zone receiving a direct-charge mixture and discharging a discharge mixture relatively poorer in the more-soluble components oi said direct charge mixture and with the other of said zones being a diffusate zone receiving components of the rst said mixture only by diffusion through said membrane and discharging a gas having a relatively higher proportion of said more-soluble components than the corresponding directcharge mixture, passing a discharge from the diffusion zone of said inlet stage and from each of said stages lower in said series except the lowest to the charge of the diffusion zone in the next lower stage, passing a discharged diiusate from each of the diusate zones in stages lower than said inlet, `up through the one discharging into said inlet, to the charge of a diffusion zone of a higher stage which is at least the second higher stage of said series, passing a discharged diffusate from said inlet stage to an intermediate stage of an odor-concentrating section of said series of stages, passing a discharge from each of the diiusion Zones in the stages of said odorconcentrating section except that of the lowest stage thereof to the charge of the diffusion zone in the next lower stage of said section, passing at least two discharged diifusates from stages below said main inlet stage to the charges of separate diusion zones of stages in said section below the inlet stage of said section, passing a discharged diffusate from the diffusate zone of Veach of said stages of said section except that of the highest stage to the charge of a .diiusion Zone of a higher stage of said section, passing a discharge from the diiusion zone of the lowest stage of said odor-concentrating section to an intermediate stage of a hydrocarbon-concentrating section, passing a discharge from the diffusion zone oi each stage of the last said section except from the lowest stage thereof to a lower stage of said section, passing a discharged diffusate from the difusate Zone of each of said stages the last said section except the highest to the charge of the diffusion zone of a higher stage of said section, passing a discharge from the difiusion zone ofthe lowest stage of said hydrocarbon-concentration section to the charge of the diiusion zone of a stage below said main-inlet stage which is lower in said series than any stage from which a discharged diffusate is passed to said odor-concentrating section, and removing as products of the entire process a nitrogen-concentrate from the difvfusion zone of the lowest stage of the entire series, an odor-concentrate from the diffusate zone of the highest stage of said odor-concentration section, and a hydrocarbon concentrate from the diffusion zone of the highest stage of said hydrocarbon-concentration section.

1'2. A process for separating a relatively odorless hydrocarbon-rich gas from a normally gaseous mixture containing from about 10 to about 50 per cent by volume of an undesired compound of the class consisting of nitrogen, oxygen and water, not more than about 5 per centI by volume of a volatile non-hydrocarbon odorous compound and the remainder normally gaseous paraffin hydrocarbons, which comprises introducing all of such a mixture into an intermediate main-inlet stage of a series of dii-fusion stages, each said stage comprising two zones separated by a nonporous membrane in which said undesired compound, parafn hydrocarbons and odorous compound are soluble with increasing solubility in the order named with one of said zones being a diiusion zone receiving a direct charge mixture and discharging a discharge mixture relatively poorer in the more soluble components of said direct charge mixture and with the other of said zones being a difiusate zone receiving components of the rst said mixture only by diffusion through said membrane and discharging a gas having a relatively higher proportion of said more soluble components than the corresponding direct charge mixture, passing a discharge from the diffusion zone of said inlet stage and from each of said stages lower in said series except the lowest to the charge of a diiusion zone in a lower stage, passing a discharged diiusate I5 from each of the diffusate zones in stages lower than said inlet up through the one discharging into said inlet to the charge of a diiusion zone of a higher stage of said series, passing a discharged diusate from said inlet stage to an intermediate stage of an odor-concentrating section of said series of stages, passing a discharge from each of the diffusion zones in the stages of said odor-concentrating section except that of the lowest stage thereof to the charge of a diiusion zone of a lower stage of said section, passing a discharge diiusate from the diiusate Zone of each of said stages of said section except that of the highest stage to a charge of a diffusion Zone of a higher stage of said section, passing at least one discharged diffusate from a stage below said main-inlet stage to a charge of a diiusion Zone of a stage in said section below the inlet stages of said section, passing a discharge from the diffusion zone of the lowest stage of said odor-concentrating section to an intermediate section of a hydrocarbon-concentrating section, passing a discharge from the diffusion zone or" each stage of the last said section except from the lowest stage thereof to a lower stage of said section, passing a discharged diiusate from the diiusate Zone of each of said stages of the last said section except the highest to the charge of a diiusion Zone of a higher stage of said section, passing a discharge from the diffusion zone of the lowest stage of said hydrocarbon concentration section to the I6 charge of a diffusion zone of a stage below said main-inlet stage which is lower in said series than any stage from which a discharged diffusate is passed to said odor-concentrating section, and removing as products ofthe entire process a substantially odorless hydrocarbon-poor fraction from the diiusion zone of the lowest stage of the entire series, an odor-concentrated fraction from the diiusate zone of the highest stage of said odor-concentration section, and a hydrocarbonconcentrate from the diiusion zone of the highest stage of said hydrocarbon-concentration section.

JEAN P. JONES.

REFERENCES CITED The following references are of record in the file of this patent: l

UNITED STATES PATENTS Number Name Date 307,042 Herzog Oct. 21, 1884 1,496,757 Lewis et al June 3, 1924 2,159,434 Frey May 23, 1939 2,388,095 Stahly Oct. 30, 1945 FOREIGN PATENTS Number Country Date 266,396 Great Britain Feb. 23, 19.27 291,576 Great Britain June 7, 1928 

1. A PROCESS FOR SEPARATING A MIXTURE COMPRISING PRIMARILY NITROGEN AND AT LEAST ONE NORMALLY GASEOUS PARAFFIN HYDROCARBON INTO A NITROGENPOOR HYDROCARBON-RICH FRACTION AND A HYDROCARBON-POOR NITROGEN-RICH FRACTION, WHICH COMPRISES INTRODUCING ALL OF SAID MIXTURE INITIALLY INTO AN INTERMEDIATE STAGE OF A SERIES OF AT LEAST FIVE DIFFUSION STAGES, EACH SAID STAGE COMPRISING TWO ZONES SEPARATED BY A NON-POROUS MEMBRANE IN WHICH PARAFFIN HYDROCARBONS ARE MORE SOLUBLE THAN NITROGEN WITH ONE OF SAID ZONES BEING A DIFFUSION ZONE RECEIVING A NITROGEN-HYDROCARNON MIXTURE AS A DIRECT CHARGE AND DISCHARGING A NITROGEN-HYDROCARBON MIXTURE POORER IN HYDROCARBONS AND WITH THE OTHER OF SAID ZONES BEING A DIFFUSATE ZONE RECEIVING HYDROCARBONS ONLY BY DIFFUSION THROUGH SAID MEMBRANE AND DISCHARGING A GAS HAVING A HYDROCARBON TO NITROGEN RATIO HIGHER THAN THAT IN THE CHARGE TO SAID DIFFUSION ZONE, IN THE STAGE BELOW THE INLET STAGE PASS- 